This Phase II, randomized, open-label, trial in HIV-infected children, aged 3-16 years, will assess the safety and tolerability of the new soft-gel capsule of saquinavir (SQU), an HIV protease inhibitor, together with two nucleoside reverse transcriptase inhibitors (RTI), or with nelfinvir(NFV) and one or two nucleoside RTI's in children. Secondary aims are to assess the pharmacokinetics of the SQU and NFV combination, to evaluate HIV, CD4 and CD8 levels and to evaluate the immune reconstitution with these two regimens.